A single-core four-winding magnetic modulation current sensor and a method for eliminating oscillation thereof

Abstract

A single core four-winding magnetic modulation current sensor and a method for eliminating oscillation thereof, relating to the field of sensor technology. The single core four-winding magnetic modulation current sensor described in the present invention has a special structure, which includes a single core four-winding structure and a peripheral circuit, through the magnetic core C, the excitation winding W ex , primary winding W p , feedback winding W s and the induction winding W i Working together with peripheral circuits to form an integrated whole, this sensor eliminates oscillations by first constructing an excitation oscillation circuit based on the saturation characteristics of the magnetic core C. This signal is then filtered by a signal processing circuit and sent to an oscillation elimination circuit. This circuit eliminates voltage oscillations on the sampling resistor in the feedback loop when the single-core closed-loop feedback structure is used. This invention solves the problem of voltage oscillations on the sampling resistor in the feedback loop when the self-oscillating fluxgate method is applied to a single-core closed-loop feedback structure.

Description

Technical Field

[0001] The present invention relates to the field of sensing technology, and in particular to a single-core four-winding magnetic modulation current sensor and a method for eliminating oscillation thereof. Background Art

[0002] In recent years, with the advancement of science and technology, power electronics technology has become increasingly mature, and corresponding power electronic devices have also been introduced. The advantages of DC power supply and distribution systems have gradually become apparent. At the same time, the increasing maturity of renewable energy power generation technology and the increasing proportion of photovoltaic power generation have led to a surge in demand for DC molded case circuit breakers.

[0003] Current intelligent circuit breakers not only protect circuits but also measure the current flowing through them. DC current sensors can detect and measure current. Modularized and miniaturized, they can be placed inside DC molded case circuit breakers, enabling intelligent circuit breakers. A current sensor designed for integration into an intelligent DC molded case circuit breaker must be smaller than the internal space within the breaker and have a measurement range greater than 1.2 times the rated current of the intelligent DC molded case circuit breaker.

[0004] Current methods for measuring DC current include the shunt method, Hall effect method, giant magnetoresistance method, magneto-optical effect method, and magnetic modulation method. Considering factors such as accuracy, cost, size, and applicable scenarios, the magnetic modulation method is more suitable for DC current measurement within DC molded case circuit breakers. The self-oscillating fluxgate method, a type of magnetic modulation technology, has been widely used due to its simplicity, low cost, and lack of a square wave excitation source. However, when the self-oscillating fluxgate method is applied to a closed-loop feedback system with a single magnetic core, the oscillating wave generated by the excitation winding will also be present in the feedback winding due to the transformer effect, thereby affecting the sampled signal on the feedback resistor.

[0005] Therefore, how to solve the problem of voltage oscillation on the sampling resistor in the feedback loop when the self-oscillating fluxgate method is applied to a single-core closed-loop feedback structure is an issue that needs to be solved urgently. Summary of the Invention

[0006] The present invention aims to solve the problem of voltage oscillation on the sampling resistor in the feedback loop when the self-oscillating fluxgate method is applied to a single-core closed-loop feedback structure. A new magnetic modulation current sensor with a single-core four-winding closed-loop structure and a method for eliminating oscillation are proposed. The purpose of the present invention is to provide a solution that can be applied to the internal current measurement of DC molded case circuit breakers.

[0007] The technical solution adopted in the present invention is:

[0008] A single-core four-winding magnetic modulation current sensor, the sensor comprising a single-core four-winding structure and a peripheral circuit;

[0009] The single core four winding structure includes the core C, the excitation winding W ex , primary winding W p , feedback winding W s and the induction winding W i ; Excitation winding W ex Used to generate alternating magnetic flux to make the circuit start to oscillate. The number of turns is N ex ; Primary winding W p The winding through which the primary current to be measured flows has N turns. p Usually one turn; feedback winding W s It is the winding for closed-loop feedback. The magnetic potential generated by this winding is used to offset the magnetic potential of the primary current. The number of turns is N s ; Induction winding W i Used to induce the oscillation wave on the exciting winding, the number of turns is N i With N s same.

[0010] The peripheral circuit includes the excitation oscillation circuit ①, the signal processing circuit ②, the oscillation elimination circuit ③, the grounding resistors R1 and R2, the sampling resistor R m And MCU sampling display circuit④;

[0011] The excitation oscillation circuit ① includes comparator A1 and comparator A2;

[0012] The excitation winding W in the single core four winding ex Terminal 1 of the excitation oscillation circuit is connected to the negative input terminal of comparator A1 in ①; the excitation winding W ex Terminal 2 of the excitation oscillation circuit is connected to the output terminal of comparator A2 in the excitation oscillation circuit; terminal 9 of the excitation oscillation circuit ① is connected to terminal 9 of the signal processing circuit ②; terminal 3 of the signal processing circuit ② is connected to the feedback winding W in the single core four-winding structure. s Terminal 3 of the feedback winding W s The 4 ends of the induction winding W are connected to one end of the grounding resistor R2, and the other end of the resistor R2 is grounded; i Terminals 5 and 6 of the primary winding are connected to the two ends of the grounding resistor R1, and one end of the grounding resistor R1 is grounded; the primary winding W p Terminals 7 and 8 of the MOSFET are used to connect the current to be measured;

[0013] The 5th terminal of the oscillation elimination circuit ③ is connected to the induction winding W at the same time. i Terminal 5 of the oscillation elimination circuit and one end of the grounding resistor R1; Terminal 4 of the oscillation elimination circuit ③ is also connected to the feedback winding W s The 4th terminal of the oscillation elimination circuit is connected to one end of the ground resistor R2; the 10th terminal of the oscillation elimination circuit ③ is connected to the sampling resistor R m One end of the sampling resistor R mThe other end of the MCU sampling display circuit ④ is connected to the sampling resistor R m both ends of .

[0014] Based on the method for eliminating oscillation of a single-core four-winding magnetic modulation current sensor, the method includes the following steps:

[0015] Step 1: Construct an excitation oscillation circuit based on the saturation characteristics of the magnetic core C;

[0016] Step 2: Add signal processing circuit based on step 1;

[0017] Step 3: Add an oscillation elimination circuit based on step 2.

[0018] Preferably, the excitation oscillation circuit is constructed according to the saturation characteristics of the magnetic core in step 1, and its working process is as follows:

[0019] The alternating excitation current i is generated by the excitation oscillation circuit ① ex , the exciting core C is alternately saturated, at this time the primary winding W p The magnetic field generated by the DC to be measured flowing through the magnet will destroy the symmetry, making the excitation current i ex The waveform contains the DC component to be measured and the distorted higher harmonics, which play a role in exciting oscillation.

[0020] Preferably, in step 2, a signal processing circuit is added on the basis of step 1, and the working process is as follows:

[0021] The excitation current i that changes due to the DC current to be measured in step 1 ex The waveform of the excitation current i is processed by the signal processing circuit ②. The signal processing circuit ② ex After filtering and integration, the output is the feedback current i s ; Signal processing circuit ② filters out the excitation current i in step 1 through a low-pass filter ex The high-order harmonics in the filter are filtered out, leaving only the DC component; the DC component obtained after filtering is used as the control quantity of the integration circuit to control the dynamic balance of the system; the feedback current i output by the signal processing circuit ② s In the feedback winding W s The magnetomotive force and the current to be measured are generated in the primary winding W p The magnetomotive force generated in the circuit is equal in magnitude but opposite in direction, canceling each other out. s The value of the feedback winding W s Number of turns N s With the primary winding W p Number of turns N p The ratio of the primary winding W can be measured p The magnitude of the current flowing through.

[0022] Preferably, in step three, an oscillation elimination circuit is added on the basis of step two, and its working process is as follows:

[0023] Excitation winding W ex There is an oscillating square wave on the feedback winding W due to the transformer effect. s and the induction winding W i The corresponding induced square waves are generated on both windings; since the number of turns of the two windings is equal, the induced voltage amplitude and phase on the two windings are the same, and the induction winding W is taken i The voltage on the feedback winding W is U1. s The voltage on the induction winding is U2, which is inverted and then added to the inversion adding circuit. i The voltage on U1 is added, so that the positive and negative oscillation waves cancel each other out.

[0024] Beneficial effect: The single-core four-winding magnetic modulation current sensor of the present invention has a special structure, which includes a single-core four-winding structure and a peripheral circuit. ex , primary winding W p , feedback winding W s and the induction winding W i Working together with peripheral circuits to form an integrated whole, this sensor eliminates oscillations by first constructing an excitation oscillation circuit based on the saturation characteristics of the magnetic core. This signal is then filtered by a signal processing circuit and sent to an oscillation elimination circuit. This circuit eliminates voltage oscillations on the sampling resistor in the feedback loop when the single-core closed-loop feedback structure is used. This invention solves the problem of voltage oscillations on the sampling resistor in the feedback loop when the self-oscillating fluxgate method is applied to a single-core closed-loop feedback structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the principle framework of a single-core four-winding magnetic modulation current sensor;

[0026] Figure 2 It is a schematic diagram of a single core four-winding structure;

[0027] Figure 3 yes Figure 1 Schematic diagram of the excitation oscillation circuit in;

[0028] Figure 4 yes Figure 3 The excitation oscillation circuit in Figure 2 Schematic diagram of the connection relationship of the excitation winding;

[0029] Figure 5 is the excitation voltage V after the circuit starts oscillating ex With the excitation current i ex Waveform diagram of ;

[0030] Figure 6 yes Figure 1 Schematic diagram of the signal processing circuit in;

[0031] Figure 7 yes Figure 1 Schematic diagram of the oscillation elimination circuit in;

[0032] Figure 8 It is the voltage waveform of the two input quantities U1 and U2 in the oscillation elimination circuit;

[0033] Figure 9 This is a diagram of the oscillation elimination effect of the oscillation elimination circuit;

[0034] Figure 10 is the sampling voltage U of the current sensor designed by the present invention m and the measured current I p Linearity relationship diagram. DETAILED DESCRIPTION

[0035] Specific implementation method I. Reference Figures 1 to 9 Specifically describing this embodiment, a single-core four-winding magnetic modulation current sensor described in this embodiment includes a single-core four-winding structure and a peripheral circuit;

[0036] The single core four winding structure includes the core C, the excitation winding W ex , primary winding W p , feedback winding W s and the induction winding W i ; Excitation winding W ex Used to generate alternating magnetic flux to make the circuit start to oscillate. The number of turns is N ex ; Primary winding W p The winding through which the primary current to be measured flows has N turns. p Usually one turn; feedback winding W s It is the winding for closed-loop feedback. The magnetic potential generated by this winding is used to offset the magnetic potential of the primary current. The number of turns is N s ; Induction winding W i Used to induce the oscillation wave on the exciting winding, the number of turns is N i With N s same.

[0037] The peripheral circuit includes the excitation oscillation circuit ①, the signal processing circuit ②, the oscillation elimination circuit ③, the grounding resistors R1 and R2, the sampling resistor R m And MCU sampling display circuit④;

[0038] The excitation oscillation circuit ① includes comparator A1 and comparator A2;

[0039] The excitation winding W in the single core four winding ex Terminal 1 of the excitation oscillation circuit is connected to the negative input terminal of comparator A1 in ①; the excitation winding W ex Terminal 2 of the excitation oscillation circuit is connected to the output terminal of comparator A2 in the excitation oscillation circuit; terminal 9 of the excitation oscillation circuit ① is connected to terminal 9 of the signal processing circuit ②; terminal 3 of the signal processing circuit ② is connected to the feedback winding W in the single core four-winding structure. s Terminal 3 of the feedback winding W s The 4 ends of the induction winding W are connected to one end of the grounding resistor R2, and the other end of the resistor R2 is grounded; i Terminals 5 and 6 of the primary winding are connected to the two ends of the grounding resistor R1, and one end of the grounding resistor R1 is grounded; the primary winding W p Terminals 7 and 8 of the MOSFET are used to connect the current to be measured;

[0040] The 5th terminal of the oscillation elimination circuit ③ is connected to the induction winding W at the same time. i Terminal 5 of the oscillation elimination circuit and one end of the grounding resistor R1; Terminal 4 of the oscillation elimination circuit ③ is also connected to the feedback winding W s The 4th terminal of the oscillation elimination circuit is connected to one end of the ground resistor R2; the 10th terminal of the oscillation elimination circuit ③ is connected to the sampling resistor R m One end of the sampling resistor R m The other end of the MCU sampling display circuit ④ is connected to the sampling resistor R m both ends of .

[0041] Figure 3 、 6 , 7 respectively Figure 1 The connection relationship between the components in the excitation oscillation circuit schematic, signal processing circuit schematic, and oscillation elimination circuit schematic are shown in the figure.

[0042] Specific embodiment 2: Based on the method of eliminating oscillation of a single-core four-winding magnetic modulation current sensor described in embodiment 1, the method includes the following steps:

[0043] Step 1: Construct an excitation oscillation circuit based on the saturation characteristics of the magnetic core C;

[0044] Step 2: Add signal processing circuit based on step 1;

[0045] Step 3: Add an oscillation elimination circuit based on step 2.

[0046] Specific embodiment 3: This embodiment further illustrates the method for eliminating oscillation of a single-core four-winding magnetic modulation current sensor described in embodiment 2. In step 1, the excitation oscillation circuit is constructed according to the saturation characteristics of the magnetic core. The working process is as follows:

[0047] The alternating excitation current i is generated by the excitation oscillation circuit ① ex , the exciting core C is alternately saturated, at this time the primary winding W p The magnetic field generated by the DC to be measured flowing through the magnet will destroy the symmetry, making the excitation current i ex The waveform contains the DC component to be measured and the distorted higher harmonics, which play a role in exciting oscillation.

[0048] In this embodiment, since the magnetization curve of the magnetic core C is symmetrical about the origin, the excitation current i ex The waveform of the primary winding W is also symmetrical about the zero point, and the average value is zero within one oscillation cycle. p The magnetic field generated by the DC to be measured flowing through the magnet will destroy the symmetry, making the excitation current i ex The waveform contains the DC component to be measured and the distorted higher harmonics, completing the excitation oscillation effect.

[0049] Reference Figures 3 to 5 Explanation: According to the excitation oscillation circuit ①, an alternating excitation current i is generated. ex Method:

[0050] like Figure 3 As shown in the topology diagram, there are two branches, the upper branch is the output of the comparator A1 and the excitation winding W ex , excitation winding W ex The internal resistance R ex The lower branch is composed of the output terminal of the comparator A1, the resistor R5 and a grounded resistor R4.

[0051] The excitation oscillation circuit is connected to the excitation winding W ex After that, at the moment of power on, the positive and negative input terminals of comparator A1 may drift due to zero point, and the potential difference may not be zero. The excitation voltage V ex Assume that the output is a positive peak voltage V H At this time, the lower branch quickly establishes current through resistors R4 and R5 and reaches a stable value. The voltage on R4 is

[0052]

[0053] But the upper branch has the excitation winding W ex As an inductor, the current cannot suddenly increase, but can only increase slowly. ex Increase

[0054]

[0055] At this time, the voltage on resistor R3 is equal to that on R4. exIf the voltage continues to increase, the voltage on resistor R3 will be greater than that on R4. At this time, the voltage on the negative input of comparator A1 will be greater than the voltage on the positive input. The output voltage of the comparator will be V H Flip to -V H After the reversal, the excitation current decreases until

[0056]

[0057] After that, the voltage at the positive input of comparator A1 will be greater than the voltage at the negative input, and the output voltage of comparator A1 will turn positive again, and the excitation current i ex From decreasing to increasing. After that, the circuit repeats the previous process and performs periodic oscillation. ex It is a square wave with alternating positive and negative currents, and the excitation current i ex Alternately rise and fall. Figure 5 shown.

[0058] Specific embodiment 4: This embodiment further illustrates the method for eliminating oscillation of a single-core four-winding magnetic modulation current sensor described in embodiment 2. In step 2, a signal processing circuit is added to step 1. The working process is as follows:

[0059] The excitation current i that changes due to the DC current to be measured in step 1 ex The waveform of the excitation current i is processed by the signal processing circuit ②. The signal processing circuit ② ex Filtering and integration are performed to isolate the feedback winding W s and integrating circuit, and is used to prevent the feedback winding W s The voltage on the integrator circuit affects the signal processing circuit ② through the low-pass filter to filter out the excitation current i in step 1. ex The high-order harmonics in the filter are filtered out, leaving only the DC component; the DC component obtained after filtering is used as the control quantity of the integration circuit to control the dynamic balance of the system; the feedback current i output by the signal processing circuit ② s In the feedback winding W s The magnetomotive force and the current to be measured are generated in the primary winding W p The magnetomotive force generated in the circuit is equal in magnitude but opposite in direction, canceling each other out. s The value of the feedback winding W s Number of turns N s With the primary winding W p Number of turns N p The ratio of the primary winding W can be measured p The magnitude of the current flowing through.

[0060] According to the signal processing circuit②, the excitation current i exAfter filtering and integration, the output is the feedback current i s , Figure 6 In the circuit, resistor R6 and capacitor C1 form a low-pass filter to filter out high-order harmonics; resistors R7, R8, R9, capacitor C2 and comparator A3 form an integrating circuit; the wiring of comparator A4 forms a voltage follower, which is used to isolate the feedback winding W s and integrator circuits.

[0061] Specific embodiment 5: This embodiment further illustrates the method for eliminating oscillation of a single-core four-winding magnetic modulation current sensor described in embodiment 2. In step 3, an oscillation elimination circuit is added to step 2. The working process is as follows:

[0062] Excitation winding W ex There is an oscillating square wave on the feedback winding W due to the transformer effect. s and the induction winding W i The corresponding induced square waves are generated on both windings; since the number of turns of the two windings is equal, the induced voltage amplitude and phase on the two windings are the same, and the induction winding W is taken i The voltage on the feedback winding W is U1. s The voltage on the induction winding is U2, which is inverted and then added to the inversion adding circuit. i The voltage on U1 is added, so that the positive and negative oscillation waves cancel each other out.

[0063] In this embodiment, after the signal processing circuit is constructed in step 2, the excitation current i ex Converted into feedback current i s Feedback current i s The value of can be obtained by the MCU sampling display circuit through the grounding resistor R2 = 1Ω. s The voltage generated on R2 and the oscillation wave generated by the transformer effect are coupled to each other, affecting the sampling results of the MCU. The oscillation elimination circuit can eliminate the oscillation wave on R2. The waveforms of the two are as follows Figure 8 As shown (the upper curve is the feedback winding W s The voltage waveform on the top and the curve below are the induction winding W i The voltage waveform on the induction winding W i The voltage on the feedback winding W is U1. s The voltage on the output is U2, which is inverted and then added to U1 through the inverting addition circuit, so that the positive and negative oscillation waves cancel each other out. Figure 9 As shown (the square waveform is the voltage waveform on the resistor R2, and the slightly curved line is the resistor R m The voltage waveform on the resistor R mThe waveform is the result after the oscillation is eliminated. At this point, the single-core four-winding magnetic modulation current sensor and the oscillation elimination method are completed.

[0064] In the oscillation elimination circuit, the wiring of comparator A5 forms a voltage follower, which is used to connect the inductive winding W i Take out the voltage U1; resistor R 10 、R 11 、R 12 The comparator A6 forms an inverting proportional amplifier circuit, which is used to extract the reverse voltage from the resistor R2; the resistor R 13 、R 14 、R 15 、R 16 Together with comparator A7, it forms an inverting addition circuit, which adds voltages U1 and U2 to eliminate the oscillation wave.

[0065] Theoretical calculation to eliminate oscillation:

[0066] Assume that the induction winding W i The voltage on the feedback winding W is U1. s The voltage on

[0067] U2=U1+i s R2

[0068] Output value U of the oscillation elimination circuit m for:

[0069] U m =-(U1-U2)

[0070] =-(U1-U1-i s R2)

[0071] =i s R2

[0072] The output value U m Through the sampling resistor R m It can be sampled and displayed by MCU. Since R2 = 1Ω, the sampled value U m Equal to the feedback current i s The value of .

[0073] like Figure 8 In the simulation experiment, the excitation winding W ex Number of turns N ex =500, primary winding W p Number of turns N p =1, feedback winding W s Number of turns N s and the induction winding W i Number of turns N iWhen the primary current is 240A, according to the feedback winding W s Number of turns N s With the primary winding W p Number of turns N p The theoretical voltage of U2 should be a straight line with a value of 2.4V, but it is coupled with the square wave from the transformer effect, and becomes a waveform that oscillates around 2.4V. The voltage waveform of U1 oscillates around 0V.

[0074] After the oscillation elimination circuit, if Figure 9 , R m The sampled voltage value U m It is a smooth curve and is stable at 2.4V. The sampling voltage U m Compared with the waveform of U2, its oscillation wave is almost eliminated.

[0075] According to the simulation experiment, the sampling voltage U is plotted. m With the DC under test I p The linear relationship is as follows Figure 10 The linearity is calculated as follows:

[0076] Where Y is the maximum measurement range of the sensor. ΔYmax is the maximum absolute error between the sensor output and the ideal straight line, that is, the maximum absolute value of the error between the system output and the ideal straight line.

[0077] The calculated linearity error is: 0.02%.

[0078] The present invention is described by way of several specific embodiments. It should be understood by those skilled in the art that various modifications and equivalent substitutions may be made to the present invention without departing from the scope of the present invention. In addition, various modifications may be made to the present invention for specific situations or circumstances without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but is intended to include all embodiments falling within the scope of the claims.

Claims

1. A single core four-winding magnetic modulation current sensor, characterized in that: The sensor includes a single-core four-winding structure and a peripheral circuit; The single core four winding structure includes the core C, the excitation winding W ex , primary winding W p , feedback winding W s and the induction winding W i ; Excitation winding W ex Used to generate alternating magnetic flux to make the circuit start to oscillate. The number of turns is N ex ; Primary winding W p The winding through which the primary current to be measured flows has N turns. p Usually one turn; feedback winding W s It is the winding for closed-loop feedback. The magnetic potential generated by this winding is used to offset the magnetic potential of the primary current. The number of turns is N s ; Induction winding W i Used to induce the oscillation wave on the exciting winding, the number of turns is N i With N s same; The peripheral circuit includes the excitation oscillation circuit ①, the signal processing circuit ②, the oscillation elimination circuit ③, the grounding resistors R1 and R2, the sampling resistor R m And MCU sampling display circuit④; The excitation oscillation circuit ① includes comparator A1 and comparator A2; The excitation winding W in the single core four winding ex Terminal 1 of the excitation oscillation circuit is connected to the negative input terminal of comparator A1 in ①; the excitation winding W ex Terminal 2 of the excitation oscillation circuit is connected to the output terminal of comparator A2 in the excitation oscillation circuit; terminal 9 of the excitation oscillation circuit ① is connected to terminal 9 of the signal processing circuit ②; terminal 3 of the signal processing circuit ② is connected to the feedback winding W in the single core four-winding structure. s Terminal 3 of the feedback winding W s The 4 ends of the induction winding W are connected to one end of the grounding resistor R2, and the other end of the resistor R2 is grounded; i Terminals 5 and 6 of the primary winding are connected to the two ends of the grounding resistor R1, and one end of the grounding resistor R1 is grounded; the primary winding W p Terminals 7 and 8 of the MOSFET are used to connect the current to be measured; The 5th terminal of the oscillation elimination circuit ③ is connected to the induction winding W at the same time. i Terminal 5 of the oscillation elimination circuit and one end of the grounding resistor R1; Terminal 4 of the oscillation elimination circuit ③ is also connected to the feedback winding W s The 4th terminal of the oscillation elimination circuit is connected to one end of the ground resistor R2; the 10th terminal of the oscillation elimination circuit ③ is connected to the sampling resistor R m One end of the sampling resistor R m The other end of the MCU sampling display circuit ④ is connected to the sampling resistor R m both ends of .

2. The method for eliminating oscillation of a single-core four-winding magnetic modulation current sensor according to claim 1, characterized in that: The method comprises the following steps: Step 1: Construct an excitation oscillation circuit based on the saturation characteristics of the magnetic core C; Step 2: Add signal processing circuit based on step 1; Step 3: Add an oscillation elimination circuit based on step 2.

3. The method according to claim 2, characterized in that In step 1, the excitation oscillation circuit is constructed based on the saturation characteristics of the magnetic core. The working process is as follows: The alternating excitation current i is generated by the excitation oscillation circuit ① ex , the exciting core C is alternately saturated, at this time the primary winding W p The magnetic field generated by the DC to be measured flowing through the magnet will destroy the symmetry, making the excitation current i ex The waveform contains the DC component to be measured and the distorted higher harmonics, which play a role in exciting oscillation.

4. The method according to claim 2, characterized in that In step 2, a signal processing circuit is added to step 1, and the working process is as follows: The excitation current i that changes due to the DC current to be measured in step 1 ex The waveform of the excitation current i is processed by the signal processing circuit ②. The signal processing circuit ② ex After filtering and integration, the output is the feedback current i s ; Signal processing circuit ② filters out the excitation current i in step 1 through a low-pass filter ex The high-order harmonics in the filter are filtered out, leaving only the DC component; the DC component obtained after filtering is used as the control quantity of the integration circuit to control the dynamic balance of the system; the feedback current i output by the signal processing circuit ② s In the feedback winding W s The magnetomotive force and the current to be measured are generated in the primary winding W p The magnetomotive force generated in the circuit is equal in magnitude but opposite in direction, canceling each other out. s The value of the feedback winding W s Number of turns N s With the primary winding W p Number of turns N p The ratio of the primary winding W can be measured p The magnitude of the current flowing through.

5. The method according to claim 2, characterized in that In step 3, an oscillation elimination circuit is added to step 2. The working process is as follows: Excitation winding W ex There is an oscillating square wave on the feedback winding W due to the transformer effect. s and the induction winding W i The corresponding induced square waves are generated on both windings; since the number of turns of the two windings is equal, the induced voltage amplitude and phase on the two windings are the same, and the induction winding W is taken i The voltage on the feedback winding W is U1. s The voltage on the induction winding is U2, which is inverted and then added to the inversion adding circuit. i The voltage on U1 is added, so that the positive and negative oscillation waves cancel each other out.

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